JAKARTA  Indonesia will replant huge swathes of mangrove forest along its vulnerable coastline to help provide a buffer against possible future tsunamis, the forestry minister said.

Environmental experts say Southeast Asia's mangroves -- many of which have been ripped out to make room for shrimp and fish farms -- could have helped slow the Dec. 26 tsunami by providing a barrier between the killer waves and land.

Forestry Minister Malam Sambat Kaban said Indonesia would revive its mangrove coastal defenses, earmarking some 600,000 hectares of mangrove across the country for revitalisation.

In the northern province of Aceh on Sumatra, where more than 110,000 people were killed in the tsunami, the government plans to replant at least 30,000 hectares with the trees.

"The tsunami in Aceh made us see the need to speed up this process," Kaban said.

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Mangroves are a family of evergreen trees and shrubs which grow on stilt-like roots in dense thickets in coastal areas, providing both a barrier to extreme weather and a rich ecosystem for marine life.

Following the December disaster a number of Asian nations have taken a new look at their struggling mangroves. Malaysia has called for mangroves to be protected from coastal development.

Kaban estimated Indonesia had lost about 30 percent of its total mangrove forest over the past several decades, much of it to commercial fish farms.

He said the reforestation plan would cost an initial 200 billion rupiah ($22 million), with planting due to start by April, and would be accompanied by outreach to local communities on the importance of preserving the mangroves.

"We will see the results in 5 years, and within 10 years they will be big and healthy," he said.

"With reforestation, we will ensure the peoples' needs are still catered for. People should still be able to farm fish outside the area."

Experts Cautious

Some mangrove experts voiced caution, however, saying previous "re-greening" projects had in fact hurt mangrove ecosystems because they were done without sufficient preparation.

Alfredo Quarto of the U.S.-based Mangrove Action Project said mangrove restoration projects in Thailand had ripped out living mangrove trees to plant seedlings of a uniform type -- a "plantation-style" approach that harmed biodiversity.

"They planted the mangroves in places where they didn't grow, and sometimes they tore down healthy mangroves to put in their own ... it was a terrible job and had very low success," Quarto told Reuters by telephone.

"It might look like a success after the first year, but after you come back in two or three years everything is dead. You have to look at 20 year periods," he said.

Quarto said successful mangrove restoration almost always involved local communities rather than government bureaucrats, and that reintroducing different species of mangroves was the key to re-establishing the forests as viable ecosystems.

Tsunami defense preparations should include a range of coastal restoration projects including mangroves, sand dunes and indigenous fringe forests, all of which have suffered as humans move closer to the sea, he said.

Kaban said Indonesia knew mangroves were only part of its coastal defenses, and said the planting programme would include other trees such as pine and almond. But he stressed that, after years of being seen as little more than a seaside pest, mangroves were increasingly important.

"The north coast of Aceh has good mangroves. In Simeuleu island, there are very good mangroves and it was the area with the smallest number of victims when the tsunami hit. The mangroves protected the island."